ISOLATION OF AUXOTROPHIC AND NIF-MUTANTS OF BACILLUS AZOTOFIXANS

Auxotrophic and Nif- mutants of Bacillus azotofixans were obtained fro m EMS mutagenized cultures using a penicillin enrichment method develo ped for this microorganism. The frequency of isolation of auxotrophic mutants (0.19%) was three times higher than that obtained for the Nif- mutants (0.063%), although both frequencies were extremely low. Most a uxotrophic mutants (8) required amino acids for growth; 3 required nit rogeneous bases and 2 required vitamins. These mutants will be used in further experiments of gene transfer with the aim of locating the nif genes on the bacterial chromosome of this species.